The present invention relates to covers or tarping systems for open-topped containers, and more specifically to an actuation mechanism for pivoting the cover over a truck bed.
Some hauling vehicles, such as dump trucks, include open-topped containers used for hauling or storing various materials. For example, in a typical dump truck application, the dump body is used to haul a variety of particulate material, such as gravel, aggregate or similar products. In addition, some hauling vehicles carry organic materials, such as grain or produce.
Depending upon the nature of the materials stored in the open-topped container, it is often desirable to provide a cover for the container. Of course, rigid covers are well known that may be hinged from one end of the container body. These rigid covers have gradually given way in the industry to flexible tarping systems because the flexible tarpaulin can be easily stowed when a cover is not necessary, such as when the dump bed is being loaded. Moreover, the flexible tarp is much easier to deploy than a rigid cover.
One tarping system for use with dump trucks is the EASY COVER® Tarping System, of Aero Industries, Inc. The EASY COVER® Tarping System includes a U-shaped bail member that is pivotally mounted at its ends to the base of the container body. The horizontal section of the U-shaped bail is attached to the tarp, while the free ends of the vertical elements are pivotally mounted.
As shown in FIG. 1, a vehicle 10 having an open-topped dump body 11, such as a dump truck, includes a tarpaulin cover 12, which is shown in its deployed configuration spanning the length of the container. The tarp cover 12 is wound onto a tarp roller 14 at the forward end of the bed.
A U-shaped bail member 16 is connected to one end of the tarp cover 12 and is pivotally mounted to the truck body 11 by way of an actuation mechanism 20. This actuation mechanism can take a variety of forms including extension springs, compression spring, and coil torsion springs which apply a torque or moment to arms 17 of the U-shaped bail member 16. When the actuation mechanism is released, it automatically pivots the bar, thereby unfurling the tarp from the tarp roller 14. A hand crank or powered motor can be provided to rotate the tarp roller in the opposite direction to wind the tarp onto the roller when it is desired to open the container top. The hand crank or motor mechanism must be capable of providing sufficient mechanical advantage to overcome the deployment force of the actuation mechanism.
One such actuation mechanism implemented in the Easy Cover® Tarping System incorporates a “double-coil” spring as more fully described in U.S. Pat. No. 6,318,790 to Henning, the disclosure of which is incorporated herein by reference. As shown in FIG. 2, this actuation mechanism 20 includes an elastically deformable double-coil spring 21 with two coil portions 23 and 24 concentrically wound around each other and disposed in a common plane with an integral center anchor section 28 between each of the coil portions 23 and 24. Each of the coil portions include a free reaction end connected to arm 17 of the bail member 16 through a pair of reaction posts 26 and 27 mounted on the arm. The center anchor section 28 is held fixed relative to the pivoting bail arm 17 and is generally fixed to the dump body 11 by a pivot shaft 18 mounted thereto. The double-coil spring 21 is arranged to apply a torsional force to the bail arm 17 to deploy the tarp cover 16, as described above.
As shown in FIG. 3, the mechanism 20 includes a housing 32 that sandwiches the double coil spring 21 between opposed housing halves. After the spring is fitted into the housing halves, the reaction posts 26 and 27 extend through openings in the housing halves. The pivot shaft 18 passes through an opening in the housing 32 to engage the center anchor section 28 of the spring. It is understood that the housing pivots about the pivot shaft to pivot the bail member arm 17 secured to the housing 32.
It has been found in practice that the double coil springs of the actuation mechanism endure their greatest stress at the transition portions 35 (see FIG. 2) between the center anchor section 28 and the coil portions 23 and 24. Repeated deployment of heavy tarps by the actuation mechanism means repeated coiling and uncoiling of the spring, which may lead to eventual fatigue of the coil springs. Since metal fatigue typically occurs at a location of greatest stress, for the double coil springs the transition portion 35 is a potential site for failure.
The weight of the tarp and its deployment mechanism may be minimized to lower the stress on the springs of the actuation mechanism and to lengthen the fatigue life of the springs. Also the fatigue life of the springs can be lengthened by increasing the number of springs and the size of the springs. However, weight reduction of the tarp and its mechanism is constrained by the need to maintain a durable tarp and mechanism. Similarly, increasing the number and size of the springs is limited by cost, space and weight considerations.
Consequently, there remains a need for improvements to a double coil torsion spring actuation mechanism, and particularly to eliminate stress or fatigue points in the spring.